1. Technical Field
The present invention relates to wireless access networks, and, more particularly, to 4th generation and beyond (4+G) mobile backhaul over orthogonal frequency division multiple access/time division multiple access—passive optical networks (OFDMA/TDMA-PON).
2. Description of the Related Art
The proliferation of fourth-generation (4G) mobile devices is dramatically changing the wireless access network and its wired counterpart. As data rates swell to 100 Mb/s-1 Gb/s per cell site (as in 4G LTE (Long Term Evolution) and LTE Advanced, respectively), the achievable wireless reach drops, increasing cell density and decreasing per-cell coverage area to ˜10-20 m2. A last mile (1-2 km) 4+G mobile backhaul link is thus needed to support over 200 cells and 20+ Gb/s per-link rates. To deliver high speeds at low latency, backhaul via fiber-optic passive optical networks (PON) is highly attractive. However, using a conventional approach of deploying a wavelength per cell to keep latency low is prohibitive for 200+ cells per fiber. Likewise, using a conventional approach of assigning an optical time-domain slot per cell is prohibitive due to the high time delay (i.e., latency) it causes, as well as unpredictable delay variability (i.e., jitter), both of which are not acceptable for low-latency, low-jitter data transmission in mobile backhaul. Moreover, fully centralized digital signal processing (DSP), as in conventional digital radio over fiber (dRoF), is expedient for point-to-point/low-density scenarios, but would mandate intensive buffering and the DSP equivalent of a long-haul transceiver at the traffic aggregation point of each 4+G backhaul link to satisfy latency constraints.
A prominent conventional approach has been to dedicate an optical wavelength per each wireless base station. The resulting architecture is a Passive Optical Network (PON) which requires at least one wavelength for every wireless base station. Although several variants of a PON approach for mobile backhaul exist, they either obviate the possibility for sub-wavelength statistical bandwidth multiplexing, incur prohibitive latency and jitter during transmission, and/or require at least one dedicated wavelength per base station. Indeed, to enable low-latency mobile backhaul for a femtocell network with ˜1000 base stations using the conventional wavelength-per-cell approach, 1000 wavelengths would be needed, which creates tremendous network management issues. Finally, the wavelength-per-cell PON approach can also increase cost and complexity due to the need for wavelength-customized hardware, which results in significant wavelength management and component inventory challenges.